Refrigeration cycle apparatuses have been known in which a refrigerant circuit is formed by connecting a plurality of use side units to at least one heat-source side unit with refrigerant extension pipes. Refrigerant is injected to such type of refrigeration cycle apparatuses, in general, according to the lengths of the refrigerant extension pipes at the installation locations upon installation work of the units. However, defects may occur in the operational state of one such refrigeration cycle apparatus when the amount of filled refrigerant is inappropriate.
For example, when the amount of refrigerant is excessive, the pressure may increase in a refrigeration cycle apparatus with devices activating into a cooling operation under a high outdoor-air-temperature environment. The high pressure will invite an inevitable interruption for safety of the device operation, leaving a state in which the device operations are non-continuable. Contrarily, where the amount of refrigerant is short, the apparatus cannot obtain the desirable cooling or heating capacity for providing user comfort.
Hence, attempts have been made to develop technology of detecting whether an appropriate amount of refrigerant is filled in the refrigeration cycle apparatus (see, for example, Patent Literatures 1 and 2).
Patent Literature 1 discloses a method for determining the appropriateness in the amount of refrigerant filled in a refrigeration circuit. The method corrects the degree of supercooling by using a supercooling degree correction value, which is obtained by dividing the degree of supercooling by a value obtained by subtracting the outdoor temperature from the condensing temperature.
Patent Literature 2 discloses another method for determining the appropriateness in the amount of refrigerant filled in a refrigerant circuit. The method uses an equation representing the relationship between the amount of refrigerant in each part of a refrigerant circuit divided into a plurality of parts, and the amount of refrigerant flowing in the refrigerant circuit or an operational state amount of each constituent devices of the refrigerant circuit.